n a world characterized by rapid change and uncertainty, the sustainable management of water resources demands a holistic and interdisciplinary approach, integrating participatory science. However, few methodologies effectively capture the complex interplay of socio-economic, biophysical, and policy factors at the scale of river basins, essential for addressing agro-ecological sustainability goals. In this study, we present an innovative modeling approach applied to a coastal river basin, combining open-source tools with the well-established SWAT (Soil and Water Assessment Tool) and System Dynamics (SD) VENSIM PLE models. The simulated discharge data closely match the observed values, showing good agreement during both calibration and validation phases, with NSE values of 0.83 and 0.75 during calibration and validation, respectively, and R2 values of 0.85 and 0.78 respectively; the simulated potential evapotranspiration also in agreement with the observed PET. Integrating calibrated hydrometeorological SWAT model outputs, including Evapotranspiration, Groundwater, Soil Moisture, and Water Streamflows, into the SD model allowed for optimization of corresponding variables, serving as pseudo-observations in the coarser SD model. This integration of 1988-2020 duration was particularly valuable in data-scarce environments with long hydrometeorological data series, enabling adjustment of SD "physical" variables. Furthermore, the finer temporal resolution of the SWAT daily time step enhanced accuracy compared to the SD monthly time step, mitigating issues such as zero surface runoff values, especially crucial in water-scarce contexts. Overall, our approach facilitates the identification of management strategies to alleviate water use conflicts and promote territorial development. By utilizing open-source models, this methodology offers flexible solutions without necessitating specific model development, thereby aiding decision-making processes and holding promise for application in diverse contexts.